This invention relates to a process for producing ethylphenol and acetaldehyde from diethylbenzene. It relates more particularly to a process for separating pure ethylphenol and recovering pure unreacted diethylbenzene from the products resulting from the decomposition of the diethylbenzene mono-hydroperoxide produced in the first step of the process.
Diethylbenzene is converted into ethylphenol and acetaldehyde by a process having two primary steps. These steps are the autoxidation of diethylbenzene to diethylbenzene monohydroperoxide and the decomposition of the diethylbenzene monohydroperoxide into ethylphenol and acetaldehyde. Such a process is described in U.S. Pat. application Ser. No. 334,084, now U.S. Pat. No. 3,923,909, filed on Feb. 20, 1974. The reactions involved in the process are as follows: ##STR1## The diethylbenzene feed may be any isomeric mixture or any pure isomer, i.e., m-diethylbenzene which is converted to m-ethylphenol.
The decomposition of the monohydroperoxide produced in the first step proceeds easily in the presence of a strong acid which does not interfere with the reaction and in the presence of a solvent. Such solvent usually is a low molecular weight aliphatic alcohol or ketone. Preferably, this decomposition reaction is carried out in the presence of sulfuric acid and an anhydrous ketone.
The selectivity of the above process with respect to the production of diethylbenzene monohydroperoxide depends on different factors, more particularly, on the degree of conversion, which preferably ranges between 5 and 30%. It therefore is necessary that unreacted diethylbenzene be recovered as completely as possible for recycle. However, this diethylbenzene must be recovered in a high degree of purity and particularly, must be free from any phenolic compound which would inhibit oxidation. It also is necessary that the ethylphenol product which is used for producing pharmaceutical products, stabilizers and other valuable derivatives, be recovered as pure as possible.
The decomposition mixture containing ethylphenol and unreacted diethylbenzene is a rather complex system. In addition, to light components (acetaldehyde, ketone, water) which are easily removed, the mixture contains other components which may be roughly divided into three groups: (1), unreacted diethylbenzene, ethylphenol and oxygenated by-products, i.e. ethylacetophenone and 1-(ethylphenyl)ethanol; (2), heavier by-products such as diacetylbenzene, 1-(acetylphenyl)ethanol, resorcinol, etc. and (3), non-volatile compounds consisting of salts and tarry materials. By using known methods, such as vacuum evaporation, steam distillation and fractional distillation, the compounds of the first group are easily separated from the others. It is then necessary to recover substantially pure ethylphenol and diethylbenzene from the mixture containing such compounds together with the oxygenated by-products. Diethylbenzene, which is more volatile than the other components of the mixture, can easily be separated by distillation. However, further resolution of the mixture by distillation is impossible because of the formation of an azeotrope between ethylphenol and the oxygenated by-products.
Methods are known which can be used to separate ethylphenol from the by-products. For instance, since ethylphenol is an acidic compound, it can be extracted by a strong base, e.g. by an aqueous solution of NaOH or KOH. Generally, phase separation does not take place upon such treatment, unless an appropriate solvent, which may be diethylbenzene, is used. Ethylphenol is then regenerated by treating the aqueous phase by an acid. However, the by-products are not completely eliminated, even after many successive washings, so that a careful distillation is still required to obtain pure ethylphenol. Moreover, another disadvantage is that this process consumes large amounts of base and of acid.
Another method which can be employed comprises carrying out an extractive distillation with a compound such as triethyleneglycol, triethanolamine or any tertiary amine, for example tri-n-octylamine, capable of association with ethylphenol. By so doing, the relative volatility of ethylphenol is sufficiently lowered for the by-products to be removed overhead. However, this extractive distillation is unsatisfactory in that it requires the use of large amounts of extracting agent and of a very efficient distillation column. Also, it is often difficult to avoid loss of some ethylphenol overhead. Moreover, ethylphenol which is withdrawn as bottoms still needs a further distillation to be obtained in the desired purity.
It is now an object of the present invention to provide a simple and efficient process for recovering pure ethylphenol from a mixture containing diethylbenzene, ethylphenol and the oxygenated by-products thereof.
It is an additional object of the present invention to provide a method for recovering pure diethylbenzene and pure ethylphenol from a prepurified mixture resulting from the decomposition of diethylbenzene monohydroperoxide.